Frequency synthesizer for broadcast telephone system having multiple assignable frequency channels

Claim 1

In a broadcast telephone system for communicating information signals over an assigned frequency channel, the combination of a synthesizer for generating a signal at the assigned frequency and a read-only memory (ROM) storing a plurality of sets of first and second signals associated with different predetermined assignable frequencies, the synthesizer comprising a first phase-locked loop, including a first voltage-controlled oscillator (VCO) for generating an output signal at a frequency within a first predetermined range including the plurality of assignable frequencies; a mixer for mixing the output signal from the first VCO with a first frequency reference signal having a predetermined frequency that is derived from a common reference frequency signal; a low-pass filter for passing the low-frequency product from the mixer; a first phase comparator for comparing the passed low-frequency product with a second reference frequency signal having a frequency within a second predetermined range and derived from a second phase-locked loop, and for providing a first voltage signal indicating the result of said comparison; and a first band-pass filter for passing the first voltage signal to the first VCO for controlling the first VCO, wherein the passband of the first band-pass filter is adapted for minimizing phase noise and electronic noise due to microphonics; a second phase-locked loop, including a second VCO for generating a third reference frequency signal within a third predetermined range; a first frequency divider coupled to the ROM for dividing the frequency of the output signal from the second VCO by an amount indicated by a first signal from the ROM associated with a given assignable frequency; a second phase comparator for comparing the divided output signal from the second VCO with a fourth frequency reference signal having a predetermined frequency that is derived from said common frequency reference signal and for providing a second voltage signal indicating the result of said comparison; and a second band-pass filter for passing the second voltage signal to the second VCO for controlling the second VCO, wherein the passband of the second band-pass filter is adapted for minimizing phase noise and electronic noise due to microphonics; and a second frequency divider coupled to the ROM for dividing the frequency of the output signal from the second VCO by an amount indicated by a second signal from the ROM associated with said given assignable frequency to provide the second reference frequency signal to the first phase comparator.